1. Field of the Invention
The present invention relates to a semiconductor laser and, more particularly, to an optically pumped semiconductor laser.
2. Description of Related Art
In general, three colors R (red), G (green) and B (blue) in the visible light region (380 nm to 760 nm) can be obtained using a semiconductor laser or non-linear second light source of wavelengths 635 nm, 532 nm, and 455 nm, respectively. Red and blue light can be obtained directly by a semiconductor laser, while green light can be obtained by a non-linear second light source. However, it is advantageous to obtain the blue light using the non-linear second light source.
Red light (635 nm) can be directly obtained by a laser of tens of milliwatts (mW) fabricated by growing an AlGaInP active layer on a GaAs substrate. On the other hand, green light (532 nm) or blue light (455 nm) can be obtained through second harmonic generation (SHG) by passing an infrared laser of 1064 nm or 920 nm through a nonlinear crystal.
Recently, a vertical extended cavity surface-emitting laser (VECSEL) having high efficiency is attracting attention as a new technology. The VECSEL includes a semiconductor epitaxy structure having a distributed Bragg reflector mirror (DBR), an active layer, such as a quantum well, a cladding window and a resonator with an output mirror. A nonlinear crystal is inserted into the resonator to obtain intracavity-type second harmonic generation (SHG).
The VECSEL is classified as an optically pumped semiconductor laser for exciting semiconductor epitaxy through optical pumping, which is available from Coherent Inc. A second type of VECSEL is referred to as a Novalux VECSEL (NECSEL) employing an electric injection type, which is available from Novalux Inc.
A conventional optically pumped semiconductor laser is disclosed in U.S. Pat. No. 5,991,318, entitled “Intracavity Frequency-Converted Optically Pumped Semiconductor Laser”. The '318 patent describes a method of introducing pumped light at an angle inclined to a surface. However, when a pumped light source of '318 patent and the epitaxy structure are adjacent to each other, it is difficult to miniaturize the laser as a focusing lens blocks infrared light.
Further, it is difficult to conform an optical axis of light generated by a resonator to an optical axis of the pumped light, i.e., the source light applied from the light source. When the optical axes are not aligned to each other optical pumping efficiency is decreased dependent upon the degree of difference as a pumped light incident region is different from the position of light generated by the resonator.
Further, although the optical axes may be aligned to each other, when the shape of the light generated by the resonator is different from that of the pumped incident light, optical pumping efficiency may be also decreased.